The present invention relates to a lens driving device and an image pickup device using it.
Conventionally, various lens driving mechanisms for driving two or more sets of lens elements of, for example, a zoom lens in the direction of an optical axis of the lens by an actuator have been proposed. FIG. 14 is a schematic perspective view of a conventional lens driving mechanism (see Japanese Unexamined Patent Publication No. 2002-131611) for driving two or more sets of lens elements. In the figure, +Z side is the image pickup element side, and −Z side is the subject side.
In the lens driving mechanism shown in FIG. 14, a first lens holder 2 holding a first set of lens elements 1 and a second lens holder 4 holding a second set of lens elements 3 are guided by a guide shaft 5 to be moved in the direction of the optical axis (Z-axis). On a diagonally upper part of the first lens holder 2 there is provided an upper protrusion 6, with which a driving shaft 8 is brought into sliding contact by the elastic force of a plate spring 7. One end of the driving shaft 8 is fixed to a pedestal 9. The driving shaft 8 is driven to move relative to the pedestal 9 in the optical axis direction by a piezoelectric device 10. The second lens holder 4 is also provided with an upper protrusion 11 on a diagonally upper part of it. The upper protrusion 11 has sliding contact with a driving shaft 12, one end of which is fixed to a pedestal 13. The driving shaft 12 is driven to move in the optical axis direction relative to the pedestal 13 by a piezoelectric device 14.
More specifically, the first set of lens elements 1 is driven to move along the driving shaft 8 and the guide shaft 5 by application of a voltage to the piezoelectric device 10, and the second set of lens elements 2 is driven to move along the driving shaft 12 and the guide shaft 5 by application of a voltage to the piezoelectric device 14. The piezoelectric device 10 and pedestal 9 for the first set of lens elements 1 are disposed on the second lens side (image pickup element (not shown) side) of the first set of lens elements 1 in the direction of the optical axis. Furthermore, the piezoelectric device 14 and pedestal 13 for the second set of lens elements 3 are disposed on the first lens side (subject side) of the second set of lens elements 3 in the direction of the optical axis.
The conventional lens driving mechanism has problems as described below. When a zoom camera module is mounted on small-sized portable equipment, it is necessary to reduce the length of the camera module in the optical direction. Reduction in the optical length requires size reduction in the driving mechanism, particularly reduction in the length of it in the direction of the optical axis.
FIG. 15 schematically shows arrangements of the driving system of FIG. 14. FIG. 15(a) shows an arrangement in the case that the first lens holder 2 holding the first set of lens elements 1 and the second lens holder 4 holding the second set of lens elements 3 are positioned most to the subject side. In contrast to this, FIG. 15(b) shows an arrangement in the case that the first lens holder 2 and the second lens holder 4 are positioned most to the image pickup element side.
In FIG. 15, the first lens holder 2 is moved between a position at a distance of w2 from an image pickup plane and a position at a distance of t2 from the image pickup plane. Furthermore, the second lens holder 4 is moved between a position at a distance of w3 from the image pickup plane and a position at a distance of t3 from the image pickup plane. In order to reduce the length of the camera module in the direction of the optical axis, it is necessary for the piezoelectric device 14 to be positioned as near the image pickup plane as possible. For this purpose, it is necessary that a distance X from the image pickup plane to the driving shaft 12 side end face of the piezoelectric device 14 is less than t3 and less than w2.
However, “t3” is the distance from the image pickup plane to the second lens holder 4 driven by the piezoelectric device 14 in the case that the second lens holder 4 is positioned most to the subject side. In addition, in order that the second lens holder 4 is driven to move to the position at the distance “t3”, it is necessary for the piezoelectric device 14 to be positioned to the subject side more than the position at the distance “t3”. Consequently, it is impossible that “X”, which is the distance from the image pickup plane to the driving shaft 12 side end face of the piezoelectric device 14, is made smaller than “t3”, and the length of the lens driving mechanism in the optical axis is large accordingly.
The piezoelectric device 10 transfers power to the upper protrusion 6 via the driving shaft 8 to drive the first lens holder 2 in the direction of the optical axis. Furthermore, the piezoelectric device 14 transfers power to the upper protrusion 11 via the driving shaft 12 to drive the second lens holder 4 in the direction of the optical axis. A space 15 near the image pickup plane is occupied by parts for driving the second lens holder 4 (see FIG. 14). Thus, it is difficult to locate in the space 15 electrical circuit components which are to be disposed near the image pickup plane and have heights in the direction of the optical axis.
FIG. 16 shows an arrangement in which the orientation of the piezoelectric device 14 and driving shaft 12 is opposite to the orientation of the piezoelectric device 14 and driving shaft 12 in FIG. 15. With this arrangement, it is possible that a space 18 near the image pickup plane corresponding to the space 15 in FIG. 15 is not occupied by anything. However, in this case, there is a problem that additional members 16 and 17 for transferring the power of the driving shaft 12 to the upper protrusion 11 are newly required and the whole length of the lens driving mechanism in the direction of the optical axis is larger than L in the case shown in FIG. 15 by the length d of the driving shaft 12.